The present invention relates to a structure shielding stray light at an optical waveguide module and an optical transceiver module used this structure, in particular, an optical transceiver module in which a transmitting function and a receiving function are unified by using a waveguide.
Recently, an application field of optical communication has been rapidly transferring from a trunk line to a subscriber line. An optical waveguide module using in an optical subscriber line system has been required to be small sized and low cost. Therefore, an optical transceiver module, in which a transmitting function and a receiving function are unified by using an optical waveguide module, has been widely used.
At the optical transceiver module, a laser diode (LD) for transmitting optical signals and a photo diode (PD) for receiving optical signals are integrated in one optical transceiver module. And as the optical transceiver module, there are an optical transceiver module in which transmitting and receiving optical signals are operated simultaneously, and an optical transceiver module in which transmitting optical signals and receiving optical signals are operated alternately by using time division operation.
However, at a conventional optical transceiver module in which transmitting and receiving optical signals are operated simultaneously, LD light not coupled with a waveguide core part circulates to the PD for receiving optical signals as stray light. This stray light becomes noise against the optical signals, consequently, the receiving characteristic such as receiving sensitivity of the optical transceiver module is deteriorated.
And at a conventional optical transceiver module in which transmitting and receiving optical signals are operated alternately by using the time division operation, when the stray light circulated from the LD to the PD for receiving optical signals is radiated to a part not being a receiving surface of the PD, since a diffusion time of a carrier generated in the PD is longer than a diffusion time of a carrier generated on the receiving surface, noise whose time constant is long is generated. Consequently, the receiving sensitivity of the optical transceiver module is deteriorated soon after changing the operation from transmitting to receiving.
The radiation path of the stray light circulated from the LD to the PD for receiving optical signals becomes complex because of the multiple reflection of the stray light in the waveguide. Therefore, at the conventional optical transceiver module, it was impossible to shield the stray light so that the stray light from the LD is not made to circulate to the PD for receiving optical signals.
It is therefore an object of the present invention to provide a structure shielding stray light at an optical waveguide module and an optical transceiver module used this structure, in which stray light of an LD circulated to a PD for receiving optical signals can be shielded and the deterioration of the receiving characteristic such as receiving sensitivity caused by the stray light can be prevented and the receiving characteristic can be improved.
According to the present invention, a structure shielding stray light at an optical waveguide module is provided. The structure shielding stray light at the optical waveguide module provides a waveguide pattern formed on a waveguide substrate, a laser diode (LD) mounting area formed on the waveguide substrate, a V shaped groove for mounting an optical fiber formed in the waveguide substrate, a waveguide clad formed on the upper surface of the waveguide substrate in which the waveguide pattern and the LD mounting area and the V shaped groove for mounting the optical fiber were formed, a waveguide core part, formed on the end surface of the waveguide clad, for radiating light, and a metal deposition, which covers the surfaces of the waveguide substrate and the surface of the waveguide clad except the waveguide core part and the LD mounting area and the V shaped groove for mounting the optical fiber, having a characteristic that does not make stray light transmitting through the other part of the waveguide core part penetrate and reflects the stray light, and shuts the stray light in the waveguide substrate and the waveguide clad.
According to the present invention, an optical transceiver module unifying a transmitting function and a receiving function at optical communication is provided. The optical transceiver module unifying the transmitting function and the receiving function at the optical communication provides an optical waveguide module. The optical waveguide module provides a waveguide pattern formed on a waveguide substrate, a laser diode (LD) mounting area formed on the waveguide substrate, a V shaped groove for mounting an optical fiber formed in the waveguide substrate, a waveguide clad formed on the upper surface of the waveguide substrate in which the waveguide pattern and the LD mounting area and the V shaped groove for mounting the optical fiber were formed, a waveguide core part, formed on the end surface of the waveguide clad, for radiating light, and a metal deposition, which covers the surfaces of the waveguide substrate and the surface of the waveguide clad except the waveguide core part and the LD mounting area and the V shaped groove for mounting the optical fiber, having a characteristic that does not make stray light transmitting through the other part of the waveguide core part penetrate and reflects the stray light, and shuts the stray light in the waveguide substrate and the waveguide clad.
According to the present invention, the structure shielding the stray light at the optical waveguide module is a structure in which the upper surface covered with the waveguide clad of the waveguide substrate and the bottom surface of the waveguide substrate and the sides of the waveguide substrate are covered with a metal deposition except the waveguide core part, the LD mounting area and the V shaped groove for mounting the optical fiber.
According to the present invention, the structure shielding the stray light at the optical waveguide module is a structure in which a metal deposition formed such as an evaporation method covers the waveguide substrate and the waveguide clad and shuts stray light transmitting through the other part of the waveguide core part in the waveguide substrate and the waveguide clad and does not makes the stray light penetrate to the outside of the waveguide substrate and the waveguide clad. In this case, the metal deposition does not make light of a wavelength band using in optical communication penetrate and reflects the light of the wavelength band in the optical communication.
According to the present invention, at the structure shielding the stray light at the optical waveguide module, instead of using the metal deposition, a resin coat, which does not makes the light of the wavelength band using in the optical communication penetrate and reflect or absorbs the light using in the optical communication, can be used.
According to the present invention, the stray light not coupled to the waveguide core part and radiated to the inside of the waveguide substrate and the waveguide clad is not made to radiate to the outside of the waveguide substrate and the waveguide clad and can be shut in the waveguide substrate and the waveguide clad. Therefore, at the optical transceiver module in which transmitting and receiving optical signals are operated simultaneously, the stray light can not be circulated from the LD to the PD for receiving optical signals. Consequently, the deterioration of the receiving characteristic such as the receiving sensitivity caused by the stray light can be prevented and improved.
According to the present invention, at the structure shielding the stray light at the optical waveguide module, optical signals from the optical fiber can be received because the waveguide core part is not covered with the metal deposition, therefore, the function to receive the optical signals is not damaged and only the stray light from the LD can be shielded. And at the structure to coat the resin material, the same effect that the metal deposition has can be obtained.
According to the present invention, at the structure shielding the stray light at the optical waveguide module, forming the metal deposition on the surfaces of the waveguide substrate and the waveguide clad can be performed with forming electrodes of the LD mounting area at the same time, therefore, any additional forming process is not be required. In case that the resin material is used, by masking the LD mounting area and the waveguide core part, and the V shaped groove for mounting the optical fiber, the resin material can be coated easily at the same time, therefore, the shielding structure can be added easily.